I think it was liquid fuel in the braziers that was spreading.
Or go out through the ceiling. IDK what it was made of, but some sort of grass would be the most logical, considering how much that material is used in book Dothraki structures.

But even if you stipulate the verisimilitude of the deaths of the Khals, having everyone kneel to Daenerys is one of the more blatant examples of forcing the plot along. Based on prior characterizations, why would parochial, barbaric, sexist warriors, with an established intolerance for witchcraft, not immediately try poking holes in any woman who emerged unharmed from a fire that killed their leadership? The worst way to take command of a group of Dothraki without some prior established authority is to kill the khal, because all the khalakas and khos will be too busy fighting for his slot to pay any attention to you. A woman whose entire history of agency within the Dothraki nation has entailed nothing but witchcraft and forbidding warriors the rightful spoils of victory is the last person they would follow in such circumstances. Her original band of Dothraki (can anyone recall seeing any of them since she came to Meereen? ) bowed down because they were the cast-off remnants none of Drogo's diadochi wanted in their khalasars, so they had no other options, plus she was breastfeeding dragons. There is almost none of that applying to the situation in Vaes Dothrak.

And of course, the plot forcing. Daenerys wins because they SAY so! Anyone who objects must be sexist!

And the anti-sexism stuff on this show is one of the most profoundly hypocritical positions I can recall seeing a TV show take, given their own history. It's made even worse when you compare them to the books. In the books, women mostly wore medieval style dresses and gowns that covered them up, instead of made-up garments that hung off their necks like childrens' bedsheet-togas, or whatever those absurd things that Cersei wears which make her look like an uncircumcised penis. In the books there was no Roz, who served no function other than nudity and titillation, before starring in a couple episodes of Joffrey's torture porn. At every turn the show has escalated the sexual exploitation of, and violence against women. Joffrey never tortured any prostitutes or murdered them in some bizarre sexual fetish. His abuse of Sansa was almost exclusively portrayed to be at least partially motivated by a whole host of other issues, not least as a substitute for her siblings' humiliations of him in various incidents, and the one sexual reference to his torture of her was implied to be an outgrowth of natural sexual curiosity. In the books, Cersei & Jaime's encounter at Joffrey's funeral bier is unmistakably consensual, while on the show, a considerable number of critics thought it was rape. In the books, a rioter's hand grabs Sansa and the Hound cuts it off, climbs on her horse and rides with her to safety, in a scene that is only recounted after the fact by Sansa. In the books, we get the camera following her instead of the actually interesting characters in that scene, as a group of man grab her, drag her into an alley and pull up her skirt, before the Hound shows up for a bloody orgy of slaughter. Catelyn murders Walder Frey's wife, instead of his adult grandson, at the Red Wedding. Margaery is broken by the Faith, instead of being released to secular custody, and not a bit of Cersei's similar ordeal is elided. They had no need to take special efforts to be sure to show her naked, especially considering the cramped setting and large crowd, which would have made it easy to not show anything below her back and shoulders. Hell, focusing on her face might have been a better chance to highlight the psychological impact of the ordeal. For a show that enthusiastically embraces the books' tendency to have characters describe battles, instead of experience them, they really skipped out on how the books use that same technique when describing the sexual abuse and exploitation of, and violence against, women. It is difficult for a writer to describe a battle well, especially from the PoV of a single character at a time, so it makes sense for an author to have a character report on the events and outcome of battles after the fact. There is not the same limitation on visually depicting a battle (at least in a narrative sense, setting aside budgetary issues), but the show doesn't mind cheaping out and going Martin's route there. But when it comes to the degradation of the gender they pretend to be interested in empowering, we get that stuff in loving detail. Tyrion's patronage of prostitutes, and Oberyn Martell's sexuality, were both established in stream of consciousness descriptions and dialogue. They did not assassinate both men's characters by showing them wallowing in brothels when they were supposed to be attending diplomatic functions.

Another thing the show does is paint itself into corners where it needs to repeat things. Like a main character catching a supposedly loyal subordinate sleeping with an authority figure who betrayed and figuratively neutered said main character, so the protagonist killed them both. Martin only did that with Tyrion, Shae & Tywin, but the show also did the same thing with Dany, Doreah and Xaro. They significantly changed the personalities and relationships of Robb's love interest & Shae, so instead of one absurd relationship, where a character raised among the nobility has a relationship with a ignorantly shrill foreigner, who is constantly offering putdowns of him and his culture, that reveal more about her ignorance (and possibly the showrunners' ) than the culture she sees fit to belittle. In the books, Jon was in his first sexual relationship, after expecting a life of celibacy, so it was plausible that he'd just roll with that obnoxious "You know nothing, Jon Snow" (and the burr didn't help, especially when you know from other movies that Rose Leslie is perfectly capable of proper speech). But not only do they redundantly repeat that dynamic with Robb & not-Jeyne, and with Tyrion & Shae, they do it in circumstances where it is inconceivable that such sophisticated and well-educated men from a leadership class would be tongue-tied and inarticulate in the face of foreigners' ignorance. And they also made them foreign for absolutely no reason that served the story. To a TV audience, not-Jeyne coming from Volantis would have been absolutely meaningless, while to a reader, her character's behavior and attitudes make even less sense if she's a Volantene noble (who are ethnically more akin to the Targaryens than not-Jeyne's swarthy complexion).

While the books' language and diction might not have been accurate to real medieval speech and modes of thought, it does feel lived-in and different, not just people from our world wearing funny clothes (which is a problem with a lot of writers these days, including, especially IMO, Brandon Sanderson). So much of what is said, or discussed for exposition, on the show is the opposite of that, and pandering to modern fashions and ignorance. Why should a man in his forties need a lecture from his father on the importance of family honor and answering insults? Tywin butchering a deer himself does not make him cool or impressive in the context of his (or any sensible similar) culture, it makes him look like a guy with weird hobbies and a lousy sense of priorities, since there are a lot of other people who COULD be doing such tasks, but while he's skinning a deer, there's no one overseeing the army. Now there was a similar scene in the books, between Sam & Randyll Tarly, but that was in the context of a family that uses hunting motifs, as well as the father deliberately trying to intimidate his son, with a well-established squeamishness about blood and death. The Lannisters are all about cultivating a regal image, but they keep making Tywin look like an eccentric outdoorsman (such people were not respected in the aristocracy of pre-industrial societies, where pallor was admired because it signaled a person who had no need to go outside), and Cersei tromps around with no grace or dignity in her walk or bearing. Whatever their affected speech patterns, it is difficult to find two nobles with a less aristocratic demeanor.

I pretty much get through the show by assuming I'm watching something else.